Japanese Prime Minister Shinzo Abe speaks at a meeting of the Council on Economic and Fiscal Policy in Tokyo on Sept. 13.

Etsuro Honda, one of Japanese Prime Minister Shinzo Abe’s closest economic advisers, isn’t happy that the premier appears to have made up his mind to go ahead with a planned sales tax hike in April.

Arguing that the plan to raise the 5% tax to 8% next spring is a case of too-much, too-fast and will put the brakes on the economy just as it is showing budding signs of exiting 15 years of deflation, Mr. Honda has made his opposition well-known. He is instead calling for a more gradual rise of one percentage point every year, saying that the economy should be able to withstand a more incremental pace.

“Three percentage points will be a serious blow and its impact on consumer sentiment will be devastating,” Mr. Honda warned in a recent interview.

Given his concerns about the damage that the tax hike in its current form could do to the economy, it would stand to reason that he is in favor of the government taking action to cushion its impact through steps such an economic stimulus package totaling as much as Y5 trillion. After all, government officials and economists estimate that a package that size would likely siphon about two percentage points off the hike, effectively turning it into a one percentage point increase.

But Mr. Honda is worried about the collateral damage that the package could inflict on the image of Abenomics, the prime minister’s economic policy mixing aggressive monetary easing along with fiscal spending and pro-growth measures.

“It may create fresh demand, but it will hurt the image that Abenomics has brought about a ‘regime change,’” he said.

“Mr. Abe has giving off the projection that he’s parted ways with the traditional policies that have failed over the years,” Mr. Honda said. “It’s been revolutionary.”

The plan to raise the consumption tax first to 8% next April and then to 10% in October 2015, was actually made law under the previous government. But the current government still has the power to put off the plan if it deems the economy to be too weak. Mr. Honda believes that the tax hike is ill-timed and could kill off the improving signs in the economy by giving an impression that Mr. Abe has toned down his drastic policies.

Mr. Honda said the prime minister shares his concerns and that the decision to stick to the plan was a difficult one. While most public opinion surveys show a majority of voters favoring either postponing the hike or making it more gradual, any changes would require parliamentary approval. Given that the present plan was finalized after months of negotiations among political parties, reopening the issue risks slowing down discussions over other policy measures and would require tremendous political capital for Mr. Abe.

He said what was really needed was a strong message by Mr. Abe to the people that he remained committed to his “revolutionary” ways. “Something like (Franklin D.) Roosevelt’s fireside chats,” he said, referring to the former U.S. president’s series of radio addresses to the people in the 1930s and 40s.

About Japan Real Time

Japan Real Time is a newsy, concise guide to what works, what doesn’t and why in the one-time poster child for Asian development, as it struggles to keep pace with faster-growing neighbors while competing with Europe for Michelin-rated restaurants. Drawing on the expertise of The Wall Street Journal and Dow Jones Newswires, the site provides an inside track on business, politics and lifestyle in Japan as it comes to terms with being overtaken by China as the world’s second-biggest economy. You can contact the editors at japanrealtime@wsj.com